Oxidation of catechin and rutin by pentaammineruthenium(III) complexes.
The reaction of catechin and rutin with Ru(NH(3))(5)L(3+) (L = N-methylpyrazinium (pzCH(3)(+)), pyrazine (pz), and isonicotinamide (isn)) complexes underwent a two-electron oxidation on the catechol ring (B ring) with the formation of quinone products. The kinetics of the oxidation, carried out at [H(+)] = 0.01-1.0 M and pH = 4.0-7.6, suggested that the reaction process involves the rate determining one-electron oxidation of the flavonoids in the form of H(2)X (k(0)), HX(-) (k(1)), and X(2-) (k(2)) by Ru(NH(3))(5)L(3+) complexes to form the corresponding semiquinone radicals, followed by the rapid scavenge of the radicals by the Ru(III) complexes. The specific rate constants (k(0), k(1), and k(2)) were measured and the results together with the application of the Marcus theory were used to estimate the self-exchange parameters for the one-electron couples of the flavonoids, H(2)X/H(2)X(+*), HX(-)/HX(*), and X(2-)/X(-*).
Sung
Jay
J
Department of Chemistry, Tunghai Christian University, Taichung, Taiwan, ROC.
Huang
Kai-Sheng
KS
Lai
Tan-Ju
TJ
Chen
Yu-Yi
YY
Lin
Chih-Yeh
CY
Yeh
Andrew
A
Wu
Dacheng
D
D002392:Catechin / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D012428:Ruthenium / Q000737:chemistry*; D012431:Rutin / Q000737:chemistry*
D009942:Organometallic Compounds; D012431:Rutin; D012428:Ruthenium; D002392:Catechin